1. Field of the Invention
The present invention relates to a method for stabilizing a water-soluble resin composition. More particularly, this invention relates to a method for stabilizing a water-soluble resin composition which comprises adding, as a stabilizing agent, a carbonate and/or an organic carboxylate of a basic nitrogenous compound to the water-soluble composition in an amount of from about 0.01 to about 10 parts by weight based on 100 parts by weight of the resin content in the water-soluble composition, the water-soluble composition being prepared by condensation reacting an acid component consisting of 1,2,3,4-butane tetracarboxylic acid alone or a polycarboxylic acid component containing at least about 50 mol% of 1,2,3,4-butane tetracarboxylic acid and a diamine in the presence of a water-soluble solvent or, if desired, in the presence of the water-soluble solvent and water to obtain a condensation product having a residual acid value ratio of about 3 to about 50% of the acid value before condensation followed by formation of a salt of the condensation product with a basic nitrogenous compound.
2. Description of the Prior Art
Heretofore, various organic solvent-type resin solutions have been developed and are used in many fields. However, organic solvent-type resin solutions involve the release of a large amount of solvent in the production steps, e.g., heating and/or drying steps, and recently have become a problem from the standpoints of environmental pollution and environmental safety. Specifically, solvents used in the fields of electrical insulating varnishes, etc., are mainly acidic or basic solvents such as cresol, xylenol, phenols, N-methyl-pyrrolidone or the like, and there are further great problems such that the deposition of the resin solution becomes inflamed.
In order to solve the above defects, attempts have been made to make the solvent for the resin solution safer, i.e., to use water as a main component of the solvent, by employing a water solubilization method, an emulsion method, etc.
In view of the above circumstances, water-soluble compositions mainly useful as electrical insulating varnishes are disclosed in Japanese Patent Application (OPI) Nos. 40632/70 (corresponding to U.S. Patent application Ser. No. 498,020, filed Aug. 16, 1974, now U.S. Pat. No. 4,008,195), 41930/70 (corresponding to U.S. Pat. No. 3,936,404) 76196/70 (corresponding to U.S. Pat. No. 3,925,313) and 37126/71 (corresponding to U.S. Patent Application Ser. No. 617,135, filed Sept. 26, 1975 now U.S. Pat. No. 4,101,488) and Japanese Patent Publication 18463/71 (corresponding to U.S. Patent Application Ser. No. 569,427, filed Apr. 18, 1975 now U.S. Pat. No. 4,014,832).
Each of those compositions shows excellent characteristics when employed as electrical insulating varnishes, but a phenomenon occurs where the viscosity of the solution increases during storage for a long period of time in the so-called water-soluble resin solution state and in the worst occasion, the practical use thereof becomes impossible due to the increase of the viscosity of the solution.